For more than a century, lawmakers from big cities have complained that their voices are ignored in state legislatures. And, it turns out, they’re right.

(Gamm and Kousser)

Bills introduced from cities with populations over 100,000 routinely have more trouble passing than those from all other districts in a state (see graphs above, to the right). And it’s nothing new—metropolises have had it tough since the late 1800s, according to recent research from two political science professors who looked at cities in 13 states over 120 years. It’s harder for big cities to get their way legislatively.

“Big-city people had an explanation, and their explanation was this is hostility,” one of the researchers, University of Rochester professor Gerald Gamm, said. But it turns out that explanation was only partly true, he said.

The thing most correlated with the big-city disadvantage was a big delegation, Gamm and University of California, San Diego, professor Thad Kousser found. Big cities send lots of representatives to state capitols, and those delegations can be hard to unify. Hostility didn’t seem to play a big role, although a certain variety may also be at play, they found: the relative size of a city’s immigrant population was correlated with bill failure.

But other reasons for the disadvantage had no meaningful correlation. Others have suggested big cities have it tough because they tend to be liberal enclaves or simply because of rural and suburban resentment or racism aimed at cities with high minority populations. But none of those seem to be correlated with bill success.

To test their hypotheses, Gamm and Kousser worked off of a cascading series of representative samples. They used a giant database of 165,284 bills that they and other researchers compiled over the past decade. That database includes every single bill introduced every 20th year from 1881 to 2001 in 13 nationally representative states. They then took a representative sample of those bills and compared all the bills that affected a single locality or county.

The strongest correlation was that between the size of a city’s delegation and a bills’s likelihood of passage. A bill from a city represented by a single legislator had 80 percent odds of passing, they found. Add a legislator, and that fell to 64 percent odds of passing. Add another, and it dropped to 53 percent. And so on, until you reach the largest delegation in the dataset (see graph below).

(Gamm and Kousser, 2013)

Size matters, but why? The larger a city delegation gets, the less its delegates vote together, they found. Majority-party domination also declines with size. Those findings suggest that a big city suffers not just from size, but from having big delegations that can’t unify.

“If there are different bills that are really important for your city, you need to figure out how to build cohesion within your local delegation,” Gamm says.

(Gamm and Kousser)

A city’s immigrant population also mattered to bill success. Cities with a higher percentage of immigrants than their states had a tougher time passing bills than those whose immigrant populations were more in line with their state (see graph below).